Q & A of the Day - Is this electrical installation arrangement OK?

Question: We are currently testing an existing electrical installation in an office block. We have found a circuit that appears to have two separate ring mains connected together. However, fed out of the distribution board are only two twin & earth cables. The circuit is protected by a BS-EN 60898 Type B 16A MCB.

I'm aware that there is a interconnection somewhere in the office, but if we cannot find this, are there actually any departures from the regulations, bearing in mind that this is protected by a 16A MCB?

Note that the maximum measured EFLI falls well below the maximum required in BS7671:2008.

Answer: From the information provided, I assume that there is a ring within a ring circuit. It would be preferable if measures were taken to identify the wiring routes and make the circuits independent.

Using 16A circuit breakers is acceptable, providing that the likely connected load is less than this value. However, if the circuit arrangement is rectified, the protective device can be increased to 32A.

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